As will be understood by those skilled in this art, a conventional electrostatic precipitator includes casing walls, or side frames, typically enclosing a plurality of rectangular chambers and fields, and the chambers are separated by longitudinal partition frames, sometimes referred to collectively here as the casing walls. Each chamber and field includes a plurality of parallel spaced vertically extending plate-like collecting electrodes, which may, for example, be up to 50 feet in length and 15 feet in width, and a plurality of discharge electrodes supported on an electrically isolated high voltage frame assembly to keep the discharge electrodes in proper alignment with the collecting electrodes. A high voltage direct current is applied to the discharge electrodes. When particulate laden process gas is passed at low velocity through this field, the particulates in the gas stream become negatively charged in the electron field. The particles are then attracted to the positive charge on the collecting electrode surfaces. When the migration toward the surfaces of the collecting electrodes is complete, the inherent resistivity of the particles will prevent complete loss of the charge to the collecting electrode surfaces and the particles will then agglomerate on the surfaces of the collecting electrodes. The particulates are then collected in a grid of hoppers located below the collecting electrodes.
As will be understood, as an electrostatic precipitator casing ages, it typically deteriorates from the corrosive atmosphere in which it operates. Some electrostatic precipitator units that have been in operation for 30 to 40 years may exhibit significant deterioration in their structural integrity, particularly the upper girders and hot roof. Depending upon the original design configuration, application and the quality of the original installation, certain areas of the electrostatic precipitator may need to be repaired or more generally replaced. The costs associated with rebuilding an electrostatic precipitator are significant. Where repair or replacement is required, there are also significant costs associated with shutting down the electrostatic precipitator, which generally requires shutting down the process or equipment generating the waste gas stream.
Electrostatic precipitators with insulator compartments instead of the now more customary Penthouse design are more susceptible to corrosion of the hot roof area, including the top flanges of the top end frames and intermediate roof beams because of their direct exposure to severe weather conditions. Cold temperatures and cooling effects of rain and snow can accelerate corrosion by causing the internal steel temperature to drop below the Acid Dew Point of the process gases. This results in various types of acids condensing on the cold steel surfaces, resulting in oxidation, corrosion and accelerated deterioration of these components.
A major repair of the upper girders, including the top end frames and intermediate roof beams, of an electrostatic precipitator will generally require relieving the load from the girders before repairs can be made. The load on the girders includes the collecting electrodes, discharge electrodes, high voltage frames and hot roof. Thus, the present method of repair or replacement of these elements is very labor intensive, expensive and typically requires an extended plant outage to complete the work.
FIGS. 3 and 4 illustrate the upper portion of one embodiment of a conventional electrostatic precipitator. As shown in FIG. 4, the discharge electrodes 34 of the electrostatic precipitator are supported by T-bars 37 which include pipes extending through the support insulators 38 supported on the hot roof 32. The collecting electrodes 40 are supported by the anvil beams 42 shown in FIG. 4. As best shown in FIG. 3, the discharge electrodes 34 are supported by high voltage support frames 36, which are supported by the T-bars 37 on support insulators 38 on the hot roof 32. As described in more detail herein, an object of this invention is to repair the electrostatic precipitator by replacing the upper girders 60 and 62, for example, without removing the discharge and collecting electrodes 34 and 40, respectively, and potentially replacing the hot roof 32.
The method of repairing an electrostatic precipitator of this invention eliminates the requirement for removal of the discharge and collecting electrodes 34 and 40, respectively, high voltage frames, etc. of an electrostatic precipitator during repair or replacement of the upper girders and hot roof, if required. The method of repair of an electrostatic precipitator of this invention thus significantly reduces the cost of repair and the down time of the electrostatic precipitator and the equipment of apparatus generating the waste gas stream treated by the electrostatic precipitator.